1. Field of the Invention
The present invention is directed generally to a planar optical display, and, more particularly, to a multi-clad black display panel and a method of making a multi-clad black display panel.
2. Description of the Background
Video display screens typically use cathode ray tubes (CRTs) for projecting an image onto the outlet face of the screen. A typical screen of this type has a width to height ratio of 4 with 525 vertical lines of resolution. An electron beam must be scanned both horizontally and vertically on the screen to form a number of pixels, which collectively form the image. Conventional cathode ray tubes have a practical limit in size and are relatively deep to accommodate the required electron gun. Larger screen televisions are available which typically include various forms of image projection for increasing the screen image size. However, such screens may experience limited viewing angle, limited resolution, decreased brightness, and decreased contrast. In order to improve brightness, more light must be incident to the viewer and less absorbed within the unit. In order to improve contrast, it is necessary that the viewing screen be as black as possible. It is not currently possible for direct view CRT""s to be black because they utilize phosphors for forming the viewing image, and the phosphors are not black.
In U.S. Pat. No. 5,625,736, an optical panel having a plurality of stacked waveguides is rendered black using a black cladding layer between transparent cores of the waveguides. The cladding layers disclosed therein have a lower index of refraction than the waveguide cores for effectuating substantial internal reflection of the image light channeled through the cores, and thereby improve contrast. However, the dual function black cladding layer, because the layer is black in color and thus places black particles in direct contact with the core, creates a small amount of light absorption, thereby reducing the amount of total internal reflection. The maximum brightness of the image displayed on the screen is thereby reduced.
Therefore, the need exists for a display panel which provides substantially total internal reflection to improve brightness, while also providing a black screen to improve viewing contrast.
The present invention is directed to an optical display panel which provides improved viewing contrast and brightness by increasing the black area visible to a viewer, while minimizing light absorption within the panel by minimizing the exposure of black particles directly to the light. The multi-clad black display panel includes an inlet face at one end for receiving light, and an outlet screen at an opposite end for displaying the light. The inlet face is defined at one end of a transparent body formed by a plurality of waveguides, and the outlet screen is defined at an opposite end of the body and may be disposed obliquely with the inlet face. Each of the waveguides includes a core for channeling light, and the core is placed between an opposing pair of transparent cladding layers. The waveguides also have a black layer disposed between transparent cladding layers.
The present invention is also directed to a method of making a multi-clad black display panel. The method includes stacking a plurality of glass sheets, each having attached thereto opposed transparent cladding layers, with a black layer disposed between each sheet, and placing the stack against a saw and cutting the stack, using the saw, at two opposite ends at an angle to form a wedge-shaped panel having an inlet face and an outlet face.
The multi-clad black display panel solves problems experienced in the prior art by providing substantially total internal reflection, thereby improving screen brightness, while also providing a black screen to improve viewing contrast.